Process of heat treating



Oct. 20, 1931. F. A. FAHRENWALD PROCESS OF HEAT TREATING Filed June 25, 1928 FRANK A. RAMENWALD V [avez-iler Attorneys Patented oct. zo, 1931 FRANK A. FAHBENWALD, 0F CHIQAGO, ILLINOIS PROCE\SS F HEAT TREATING Application filed June 25,

This invention relates to a process for heat treating l metal strips, strands, sheets, and Wires and has for its objects the provision of a simple process for producing the requisite temperature conditions and changes in a particularly rapid, exact, and accurately controllable manner, with a minimum of injury to the surface of the articles. In the following description I have adverted chiefly. to apparatus for the heat-treatment of steel in the form of continuous sheets, since this art eX- hibits the maximum tonnage and the most severe surface requirements at the present day, but many of the considerations hereafter set forth apply to other metals and to other forms thereof.

Apparatus for this purpose has heretofore been of two kinds, either one wherein the stock is piled and heated intermittently or 2@ one wherein the sheets or strands are drawn or conveyed continuously through the heated region. The two commonest modes have been irst to support the sheet on moving rolls, and second to draw the sheet over stationary7 transverse skids. The rolls are sometimes kept cool with water and sometimes (as in my Paf/ent No. 1,623,469, April 5, 1927) maintained at the full furnace temperature. The skids when used are generally water cooled, and have to be buffed to a high polish to avoid scratching the hot sheets which pass thereover. Both these forms of apparatus are very expensive, the water-cooled because of the amount of heat removed by the water and the non-cooled because of the expense of so much high-temperature alloy, and both types because of the great length required and the heat-losses from the resulting surface area. In a case where it is necessary to reheat several times between rollings it will be seen that the area required is very great` the expense enormous, and the different rolling stations constitute practicallv separate plants.

In the drawings I have shown a few specimen embodiments of apparatus whereby my process may be performed, these drawings being of a semi-diagrammatic nature since the specific construction can vary very widely, the main features of my idea being very few in number and broad in character. .In

1928. Serial No. 287,910.

Fig. 1 I have shown an apparatus of extreme simplicity containing my improvements; Fig.

2 is a longitudinal sectional view of Fig. 3 a transverse sectional view of a strip annealing furnace containing further features of my inventlon; Fig. 4 is a vertical sectional view and Fig. 5 a horizontal sectional view of another furnace whereby my invention may be performed; and Fig. 6 illustrates a wire anneallng furnace suitable for the performance of my improved process.

In Fig. l, 10 denotes the rim or side wall of the drum, which is carried by a suitable shaft or spindle 11 preferably with spokes 12 or equivalent, the whole being housed in- 65 side a casing 13, which is formed with ingress and egress openings 14 and 15 respectively. Suitable heat sources 16, (either burners or electric resistances or even coal grates) are provided at any suitable position so as to heat 7o the casing contents. The strip or strand 18 passes over the drum, suitable guide rolls 17 being employed to wrap the strip around the drum so as to bring it into close, heat-transferring contact therewith. As a'result the 75 strip assumes the temperature of the drum surface almost instantaneously.

For the purpose of both heating and cooling the strip or strand I have provided the apparatus shown in Figs. 2 and 3, wherein so a plurality of drums are employed, s0 arranged that each shall wrap the strip about adjacent drums. Each drum has a cylindrical body 20 mounted on one or more spiders 21 carried by a shaft or spindle 22, the latter 85 preferably being supported by an axial neck 23 at one end only, said neck projecting through one wall 24 of the furnace to a suitable eXtension bearing 25. The other wall 26 of the furnace can then easily be made removable in whole or part to facilitate applying the strip initially to the drums. I have shown the furnace as having a top 30, an end 31, a partition 32. and a flue 33 the chamber between 31 and 32 constituting the high tem- 95 perature region. The metal is heated above the critical point. From the hot chamber just described the strip 34 passes to an adjoining unheated chamber in which are other drums 35. It is largely by contact with these 1U y drums that cooling is eected. It is within my invention to cool artiiciall one or more of these, such cooling being per aps best used on that drum employed to depress the temperature below the critical point; although even without this the heat loss will be facilitated by contact with the drums.

In Figs. 4 and 5 I have shown a recuperative system, the strip 40 passing over and under a series of drums 41 contained in' a vestibule 42, thence through an opening 4.3 in a partition 44 into a heating chamber 45 where it is Wrapped over one or more further drums 46, whence it passes to a reversing drum 47. rIhis last drum is preferably set upright so as to displace the strip latorally as shown in Fig. 5, so that said strip is returned to its starting point by-being wrapped about the same rolls which carried it in. As a result the heat abstracted from the chamber 45 emerging strip is delivered back to the incoming portion of the strip by conduction through the common drum. As a result of the consequent heateconomy, electric heating becomes entirely feasible and the strip is also delivered back to its starting point, thus enabling successive rolling operations in closely adjacent equipment.

In Fig. 6 I have shown my improvements as applied to a wire-treating apparatus. The drums are arranged in pairs, and are, in this case, circumferentially grooved to space and guide the wires (the same can be done with narrow strip) and the wires are wrapped about both drums of each pair. The drums are located in the heated chamber 51 and the drums 52 in the vestibule 53. The entering wire 55 is first wound in alternate grooves of the drums 52, then carried to one end of the drums 50 where it is wound thereon uniformly to the opposite end, whence it is carried to the drums 52 and wound thereon in the intermediate grooves in a proper direci tion to be ejected by the same direction of movement which feeds the untreated wire into the furnace.

rIhese drums may either be positively driven or may be idlers and driven by the strip itself which is pulled through the furnace by any suitable means, or the two types may be mingled in any desired manner, as may be found expedient.

Several metallic compositions are known which will withstand the necessary temperature without loss of form, strength or surface and I do not limit myself to any one composition, although in general the best success has been had with alloys of 10 to 30% of chromium with one or more iron group metals.

It will be understood that a great many additional features can be incorporated into the apparatus and the design and arrangement of the parts considerably changed without deaeaacae parting from my inventive idea or saericing the benets thereof and I do not limit myself in any wise except as specifically recited in my several claims which I desire may be construed broadly each independentof limitations contained in other claims.

Having thus described my invention what I claim is:

1. The improvement in the continuous process of heat-treating metallic strands which consists of first heating the same to a temperature above the critical point of the metal while supporting the same upon moving masses of metal the contacting portions of which progress at the same speed as the sheets and exhibit substantially the full maintained temperature, and then while still surrounded by aeriform Huid cooling the same quickly below the critical point of such metal while supporting the same upon and in Contact with moving masses of metal the contacting portions of which progress at the same speed as the sheets and exhibit a temperature lower than that of the surrounding aeriform fluid.

2. 'Ihe improvement in the continuous process of heat-treating metallic strands which consists of passing said strands in succession from one to another of a series of metallic masses all of which have surface portions moving forward at the same rate of speed as said strands, the first' members of the series being maintained at a higher temperature than the strands and also above the critical point of the metal of said strands whereby said metal is heated quickly above.

its critical point, and certain of the subsequent members of the series being maintained below the critical point of such metal whereby the metal of the strands is quenched.

In testimony whereof I hereunto aiix my signature.

FRANK A. FAI-IRENWALD. 

